1. Field of the Invention
The present invention relates to a switch such as circuit breaker, current limiting device or electromagnetic contactor, in which an arc may form in a housing at a time of current cutoff.
2. Description of the Prior Art
FIG. 1 is a side view showing a circuit breaker in an opening condition as an example of conventional switches, and FIG. 2 is a side view showing a condition immediately after contact opening in the circuit breaker of FIG. 1. FIG. 3 is a side view showing the maximum opening condition of a moving contact in the circuit breaker of FIG. 2. In the drawings, reference numeral 1 designates a moving contact of the circuit breaker, and the moving contact 1 is supported so as to rotate about a rotation supporting point (rotating center) 14 (see FIGS. 2 and 3) of a base portion. Reference numeral 2 designates a traveling contact secured to one end (a lower surface of a free end) of the moving contact 1, and 3 designates a stationary contact making and breaking contact with the traveling contact 2 by the rotation of the moving contact 1. Reference numeral 4 designates a fixed contact having the stationary contact 3 at one end thereof, and a configuration of the fixed contact 4 will be described later. Reference numeral 5 designates a terminal on a side of a power source, which is connected to the other end of the fixed contact 4, and 6 designates an arc-extinguishing plate which functions to stretch and cool the arc formed between the traveling contact 2 and the stationary contact 3 at an opening time therebetween. Reference numeral 7 designates an arc-extinguishing side plate holding the arc-extinguishing plates 6, and 8 designates a mechanism portion which causes the moving contact 1 to rotate. The mechanism portion 8 includes a current detecting element (not shown), and is operated according to detection of short-circuit current by the current detecting element. Reference numeral 9 designates a handle for manually operating the mechanism portion 8, 10 designates a terminal on a side of a load, and 11 is a conductor for connecting the terminal 10 to the moving contact 1. Further, reference numeral 12 designates a housing containing these circuit breaker components, and 13 designates an exhaust hole provided in a wall portion of the housing 12.
A description will now be given of the configuration of the fixed contact 4.
In FIGS. 1 to 3, the fixed contact 4 is integrally provided in a form including a conductor portion 4a connected to the terminal 5 on the side of the power source to horizontally extend, a vertical conductor portion 4b bent downward at an end of the conductor portion 4a opposed to the terminal 5, a conductor portion 4c serving as a step-shaped lower portion horizontally extending from a lower end of the conductor portion 4b toward the opposite side of the conductor portion 4a, a conductor portion 4d vertically rising from a distal end of the conductor portion 4c, and a conductor portion 4e horizontally extending from an upper end of the conductor portion 4d toward the conductor portion 4a. Further, the stationary contact 3 is mounted on the conductor portion 4e.
In the fixed contact 4 shaped as set forth above, the conductor portion 4d connecting the conductor portion 4c serving as the step-shaped lower portion to the side of the stationary contact 3 is positioned on the side of the other end of the moving contact 1, to which the traveling contact 2 is not secured with respect to the stationary contact 3, and on the side opposed to the terminal 5. The conductor portion 4e having the stationary contact 3 is positioned below a contact surface between the traveling contact 2 and the stationary contact 3 at a time of contact closing therebetween. The fixed contact 4 is used in a skin exposed condition where an entire surface thereof is not insulated.
A description will now be given of the operation.
In a condition shown in FIG. 1, the terminal 5 of the fixed contact 4 is connected to the power source, and the terminal 10 on the side of the load is connected to the load.
In this condition, if the handle 9 is operated in a direction shown by the arrow B, the mechanism portion 8 is actuated so as to downwardly rotate the moving contact 1 about the rotation supporting point 14 (see FIGS. 2 and 3) of the base portion. Thereby, a contact closing condition where the traveling contact 2 contacts the stationary contact 3 is provided to feed power from the power source to the load. In this condition, the traveling contact 2 is pressed toward the stationary contact 3 with a specified contact pressure so as to ensure reliability of power supply.
If a short-circuit event or the like occurs in a circuit on the side of the load with respect to the circuit breaker to feed a large short-circuit current into the circuit, the current detecting element in the mechanism portion 8 detects the large current so as to actuate the mechanism portion 8. The moving contact 1 is thereby rotated in a contact opening direction to open the traveling contact 2 from the stationary contact 3. At a time of the contact opening, an arc A forms between the traveling contact 2 and the stationary contact 3 as shown in FIGS. 2 and 3.
However, when the larger current such as the short-circuit current flows, extremely strong electromagnetic repulsion is generally caused on the contact surface between the traveling contact 2 and the stationary contact 3. Accordingly, the moving contact 1 is rotated in the contact opening direction before the action of the mechanism portion 8 in order to overcome the contact pressure applied to the traveling contact 2.
Therefore, the rotation causes the opening between the traveling contact 2 and the stationary contact 3 so as to stretch and cool the arc A generated between the contacts 2 and 3 by the arc-extinguishing plate 6. As a result, arc resistance increases, and a current-limiting action is generated to diminish the short-circuit current so that the arc A is extinguished at a zero point of current, resulting in completion of current cutoff.
The current-limiting action is very important for improvement of a protection function of the circuit breaker. As set forth above, it is necessary to increase the arc resistance so as to enhance a current-limiting performance.
Preferred techniques to stretch the arc so as to increase the arc resistance includes a method using a fixed contact having a shape which is disclosed in, for example, Japanese Patent Application Laid-Open Nos. 60-49533 and 2-68831.
The shape of the fixed contact disclosed in these Japanese Patent Application publications is basically identical with that of the fixed contact 4 shown in FIGS. 1 to 3.
Referring to FIGS. 1 to 3, a current path including the fixed contact 4 extends from the terminal 5 on the side of the power source to the stationary contact 3 through the conductor portions 4a, 4b, 4c, 4d and 4e in this order.
In such a current path, current in the current path 4e on the side of the stationary contact 3 of the fixed contact 4 causes electromagnetic force applied to the arc A, and the electromagnetic force serves a force to stretch the arc A toward the arc-extinguishing plate 6. As a result, it is possible to increase the arc resistance so as to provide the circuit breaker having an improved current-limiting performance.
In order to enhance the current-limiting performance in a normal AC cutoff, it is necessary to increase the arc resistance as set forth above. In this case, it is however necessary to increase the arc resistance before the current reaches the maximum value immediately after opening the contacts 2 and 3. Even if the arc resistance is increased after the current becomes large, it is difficult to limit the current due to an inertial effect of the current. Rather worse damage is caused to the breaker because arc energy generated in the breaker becomes large due to the large current and the high resistance. Consequently, it is necessary to provide the fixed contact shape which can largely stretch the arc immediately after opening the contacts 2 and 3 by the strong electromagnetic force so as to rapidly increase the arc resistance.
However, the switch having the conventional fixed contact shape is provided as set forth above. Thus, as shown in FIG. 2, only the conductor portion 4e on the side of the stationary contact 3 can serve as the current path of the fixed contact 4 which can concurrently generate the electromagnetic force exerting in a direction to open the moving contact 1 immediately after opening the contacts 2 and 3, and the electromagnetic force to stretch the arc A in the direction of the terminal 5 on the side of the power source. Other current paths (conductor portions) 4a, 4b, 4c and 4d prevent an opening action of the moving contact 1 and generate electromagnetic force to stretch the arc A on the side opposed to the terminal 5. The current in the current path 4d has the same direction as that of the current of the arc A to attract each other while the current in the current path 4b has the direction opposed to the current of the arc A to repel each other. Therefore, the arc A should be stretched in the direction opposed to the terminal 5. Further, the current in the current paths 4a and 4c flow in the direction opposed to that of the current in the current path 4e so as to generate electromagnetic force to stretch the arc A in the direction opposed to the terminal 5.
In addition, only the current path 4e of the fixed contact 4 can exert the electromagnetic force in a rotating direction on the entire moving contact 1 as set forth above. In other current paths 4a and 4c, current flows in the same direction as that of the moving contact 1 so as to exert the electromagnetic force in a direction to close the moving contact 1. The current in the current path 4d can exert the electromagnetic force in the rotating direction on the side of the rotating center 14 of the moving contact 1, but exert the electromagnetic force in the closing direction on the side of the traveling contact 2.
Accordingly, with the shape of the fixed contact 4 used in the conventional switch, there is a problem in that the electromagnetic force generated by the current in the fixed contact 4 can not effectively act in order to stretch the arc A. Further, though only the electromagnetic force by the current path 4e of the fixed contact 4 contributes to high speed opening of the moving contact 1, the electromagnetic force rapidly decreases due to an extended distance between the traveling contact 2 and the stationary contact 3 as the moving contact 1 is rotated. Additionally, there is generated a relatively large effect of the current in other current paths 4a, 4b, 4c and 4d which generate the electromagnetic force in the direction to prevent the opening action. Hence, there is another problem of a reduced speed of the opening action. As a result, there are other problems in that the opening speed is reduced, and a required current-limiting performance can not be provided.
FIG. 4 is a side view showing a closing condition of the circuit breaker serving as the conventional switch disclosed in, for example, Japanese Patent Application Laid-Open No. 60-49535. FIG. 5 is a side view showing an opening condition of only a moving element in FIG. 4, and FIG. 6 is a side view showing an opening condition of the moving element and a repelling element in FIG. 4.
In the drawings, reference numeral 101 means one electric contact (hereafter referred to as moving element) of the circuit breaker, and the moving element 101 can rotate with a supporting shaft P1 of a main end as the rotating center as shown in FIGS. 7 and 8. Reference numeral 102 designates a contact secured to a lower surface of a free end of the one moving element 101, and 103 designates the other electric contact (repelling element) disposed under the one moving element 101. The electric element 103 can also rotate with a shaft P2 of a main end as the rotating center. Reference numeral 104 designates the other contact secured to an upper surface of a free end of the other electric contact 103 so as to make and break contact with the other contact 102. The moving element 101 and the other electric contact 103 form a pair of electric contacts.
Reference numeral 105 designates a terminal of a power source system, and 106 designates a conductor electrically connecting the other electric contact 103 to the terminal 105. Reference numeral 107 means a first conductor portion horizontally extending at a position below the moving element 101, and the terminal 105 is connected to one end of the first conductor portion 107. Reference numeral 108 means a second conductor portion continuously formed with the other end of the first conductor portion 107 so as to rise at a position below the moving element 101, and the conductor 106 includes the first conductor portion 107 and the second conductor portion 108. Here, the second conductor portion 108 has flexibility so as not to prevent rotation of the electric contact 103. Further, the main end of the repelling element 103 is rotatably coupled with an upper end of the second conductor portion 108 through the shaft P2.
Reference numeral 109 means a torsion spring which is fitted with a main end coupling shaft P2 of the other electric contact 103, and 110 means a mechanism portion for rotating the moving element 101. The mechanism portion 110 has a function to automatically rotate the moving element 101 in the opening direction when current having a predetermined current value or more (short-circuit current) flows in the circuit breaker. In view of the fact, in general, the other electric element 101 is referred to as the moving element 101, and the contact 102 will be referred to as traveling contact 102.
Reference numeral 110a means a spring anchor which is provided at a side surface portion of a casing of the mechanism portion 110. One end of the torsion spring 109 anchors the spring anchor 110a, and the other end of the torsion spring 109 anchors the moving element 101. The torsion spring 109 contacts the contacts 102 and 104 with a predetermined force at a closing time. Further, a stopper (not shown) is provided for the electric contact 103 such that the other electric contact 103 is held at a position shown in FIG. 5 at an opening time of the moving element 101.
Therefore, the other electric contact 103 can rotate in the opening direction if force larger than that of the torsion spring 109 is applied to the other electric contact 103. As noted above, since the electric contact 103 can repel with a large force, the electric contact 103 will be hereafter referred to as repelling element, and the contact 104 will be referred to as repelling contact.
Reference numeral 111 means a handle for manually operating the mechanism portion 110, and the handle 110 is operated so as to manually switch the moving element 101. Reference numeral 112 means a stopper to set the maximum opening position of the repelling element 103, 113 means an arc-extinguishing plate, and 114 is an arc-extinguishing side plate holding the arc-extinguishing plate 113. Reference numeral 115 means a terminal on a side of a load, 116 means a housing containing the components of the circuit breaker, and 117 is an exhaust hole provided in a wall portion of the housing 116.
A description will now be given of the operation.
In FIG. 4, in case the one terminal 105 is connected to the power source and the other terminal 115 is connected to the load, it is possible to feed the power from the power source to the load. At this time, the traveling contact 102 and the repelling contact 104 are in a closing condition where the traveling contact 102 and the repelling contact 104 contact each other with a predetermined contact pressure by a contact pressure spring (not shown) of the moving element 101 and the torsion spring 109 of the repelling element 103. In the closing condition, current as shown in FIG. 7 flows in the moving element 101 and the repelling element 103. That is, as shown by the narrow arrow in FIG. 7, the current enters the terminal 105 to pass through the first conductor portion 107, the second conductor portion 108, the repelling element 103, and the repelling contact 104 in this order. Subsequently, the current reaches the moving element 101 after passing through a contact surface between the repelling contact 104 and the traveling contact 102. The current in the moving element 101 exits from a conductor in a vicinity of the rotating center P1 to the side of the load.
As will be clear in FIG. 7, the current in the repelling element 103 and the current in the moving element 101 are substantially parallel to each other, but have opposite directions. Accordingly, electromagnetic repulsion F is applied between the moving element 101 and the repelling element 103. The contact pressure between the traveling contact 102 and the repelling contact 104 is set to a magnitude larger than that of electromagnetic repulsion which is generated by small current such as load current or overload current. With the small current, the traveling contact 102 and the repelling contact 104 are never opened by rotating the moving element 101 or rotating the repelling element 103 without operating the mechanism portion 110.
The moving element 101 may be rotated by the handle 111 in order to cut off normal load current, and the mechanism portion 110 is automatically operated to rotate the moving element 101 to an opening position shown in FIG. 5 when the overload current flows. In either case, the repelling element 103 is never operated by the torsion spring 109 in the opening direction. This condition is shown in FIG. 8. In FIG. 8, a magnetic field generated by the current in the repelling element 103 exerts force Fm on the arc A in a direction of the arc-extinguishing plate 113. As a result, the arc A is stretched in the direction marked Fm, and is cooled and extinguished by the arc-extinguishing plate 113, resulting in completion of the current cutoff.
On the other hand, in the closing condition shown in FIG. 7, if the large current such as short-circuit current flows, the electromagnetic repulsion F applied between the moving element 101 and the repelling element 103 becomes larger than the contact pressure between the contacts 102 and 104, that is, the pressure of the torsion spring 109 or the contact pressure spring of the moving element 101. Consequently, the moving element 101 and the repelling element 103 are started to rotate in the respective opening directions.
As shown in FIG. 9, since both the moving element 101 and the repelling element 103 move in the opening directions, that is, move in each opposite direction, an interval between the traveling contact 102 and the repelling contact 104 thereof increases twice as compared with a case where only the moving element 101 is moved. In other words, the opening speed becomes twice as fast. Hence, it is possible to reach a condition where the moving element 101 and the repelling element 103 rotate to the maximum extent as shown in FIG. 10 in a short time after the short-circuit current starts to flow.
The magnetic field generated by the current in the repelling element 103 exerts the force Fm in the direction of the arc-extinguishing plate 113 on the arc A so as to stretch the arc A. As a result, it is possible to rapidly increase arc voltage, and provide an excellent current-limiting performance. Though the arc A is still generated by the current diminished by the excellent current-limiting performance, the arc A is extinguished by undergoing the cooling operation by the arc-extinguishing plate 113.
Since the conventional switch is provided as set forth above, the electromagnetic repulsion F is reliably generated between the moving element 101 and the repelling element 103 by the current path as shown in FIG. 7. However, another electromagnetic repulsion is also generated between the repelling element 103 and the first conductor portion 107, and the electromagnetic repulsion serves as force in a direction opposed to the opening direction of the repelling element 103. Further, magnetic field generated by the second conductor portion 108 exerts electromagnetic force on the repelling element 103, and the electromagnetic force also serves as force in a direction opposed to the opening direction of the repelling element 103. That is, there is a problem in that the electromagnetic force generated by the current of the moving element 101 to rotate the repelling element 103 in the opening direction may be considerably decreased by the electromagnetic force in the opposite direction generated by the current in the first and the second conductor portions 107 and 108.
As shown in FIGS. 9 and 10, as the moving element 101 and the repelling element 103 rotate in the respective opening directions, the interval therebetween becomes larger. Accordingly, electromagnetic force to rotate the moving element 101 and the repelling element 103 in the respective opening directions also becomes weak. To the contrary, intervals between the repelling element 103 and the first conductor portion 107, and between the repelling element 103 and the second conductor portion 108 are decreased. Therefore, the electromagnetic force to rotate the repelling element in the direction opposed to the opening direction becomes large. As a result, as the interval between the contacts 102 and 104 becomes large because of the rotation of the moving element 101 and repelling element 103, the electromagnetic force to rotate the moving element 101 and repelling element 103 in the opening direction is decreased. In particular, since the electromagnetic force in the direction opposed to the opening direction also increases in the repelling element 103, reduction of the electromagnetic force in the opening direction is remarkable.
In a typical arrangement in the housing 116 of the circuit breaker as shown in FIG. 4, the repelling element 103 is shorter than the moving element 101 because of the mechanism portion 110.
In general, in case the rotating center is provided at one end of a rod, moment of inertia with respect to the rotating center is proportional to the square of a length of the rod, and moment of force is proportional to the length of the rod. Accordingly, angular acceleration with respect to the rotating center is inversely proportional to the length of the rod. In case this relationship is applied to the moving element 101 and the repelling element 103, the repelling element 103 can rotate faster than the moving element 101 immediately after the short-circuit current starts to flow because the repelling element 103 is shorter than the moving element 101. Hence, it can be considered that the repelling element 103 rather than the moving element 101 greatly contributes to the increased arc length initially generated between the contacts 102 and 104, that is, the current-limiting performance.
However, in the circuit breaker having a terminal structure as set forth above, it is impossible to effectively generate electromagnetic force to rotate the repelling element 103 in the opening direction. Consequently, there is a problem in that the rotation of the repelling element 103 is slow, and rapid initial rising of the arc voltage required for the current-limiting can be obtained.
Further, the electromagnetic force to rotate the repelling element 103 in the opening direction is considerably reduced in a condition where the repelling element 103 is rotated to the maximum extent as shown in FIG. 10. Hence, the repelling element 103 easily turns back to an original position by the force of the torsion spring 109 if the electromagnetic force is slightly reduced due to reduction of the current. As a result, there are problems in that, even if the repelling element 103 is rotated to the maximum extent so as to provide the maximum arc voltage, the repelling element 103 immediately turns back, and the arc voltage is easily reduced.
The repelling element 103 exerts the electromagnetic force in the direction of the arc-extinguishing plate 113 on the arc A between the contacts 102 and 104. The current in the first conductor portion 107 exerts the electromagnetic force in the direction opposed to the arc-extinguishing plate 113 on the arc because the current in the first conductor portion 107 has a direction opposed to that of the current in the repelling element 103. Further, the current in the second conductor portion 108 and the current in the arc attract each other because of the same direction thereof. Therefore, the arc A is stretched in the direction opposed to the arc-extinguishing plate 113. Accordingly, only the current in the repelling element 103 can be used for the electromagnetic force to stretch the arc A, and other current in the first conductor portion 107 and the second conductor portion 108 exert the electromagnetic force in the opposite direction. As a result, there are problems in that the electromagnetic force extending the arc A in the direction of the arc-extinguishing plate 113 is weak, and high arc voltage can not be obtained since the arc can not be stretched.
As set forth above, in the conventional circuit breaker, there is a problem in that a sufficient current-limiting performance can not be provided due to the above causes.